The testing of integrated circuits is an important part of the manufacturing process for ensuring customer satisfaction of the final product. Many testing techniques are available, such as the standardized testing procedures approved through the Joint Test Action Group (JTAG), for checking the functionality and operation of the integrated circuit.
One feature of the integrated circuit which has proven difficult to test is the electrical continuity through the power supply bonding wires. The bonding wire is typically coupled in a path from the external package pin of the integrated circuit to a bonding pad which continues through a metal conductor to the internal power supply conductor. In most integrated circuits, especially those having a high power consumption, the internal power supply conductor receives the external power supply potential through a plurality of parallel conduction paths, each path including the aforedescribed bonding wire, bonding pad and metal conductor for distributing the current flowing therethrough. This is necessary since conventional bonding wires have relatively low current carrying capacity. Thus, one important test during manufacturing is to verify the continuity through all bonding wires to ensure an even distribution of the power supply current as designed. Should the integrated circuit be placed in service with one or more bonding wire missing or broken, the power supply current would be distributed between the remaining bonding wires thereby increasing the stress thereon. Alternately, one or more bonding wires may fail during service which would also cause undesirable stress on the remaining bonding wires. The integrated circuit may not provide optimal performance or may have a reduced service life with the remaining power supply bonding wires carrying excess current.
Conventional testing procedure might suggest simply checking the power supply potential on either side of the bonding wires, or a check continuity between the external power supply pin and the internal power supply conductor. However since both sides are bussed together, any one good connection within the plurality of bonding wires would pass such tests even with an open circuit for one or more of the other bonding wires. Thus, most if not all testing techniques for power supply bonding connections cannot detect a failure of one bonding wire within a plurality of good bonding wires. Moreover, it is difficult to detect bonding wire failures occurring after the integrated circuit is place in service.
Hence, what is needed is an improved integrated circuit having an open bond detection circuit for verifying the continuity through each and every bonding wire coupled between the external pin and the bonding pad either during manufacturing test or any time thereafter even with the integrated circuit mounted on a printed circuit board.